Composite materials where metals are mother grounds or matrixes, have been widely used in grinding or fields requiring anti-abrasion. The composite materials in those usages are required to contain as many lubricants or ground grains as possible, or to be preferable in holding those materials as well as excellent in mechanical properties such as compression strength or tensile strength. Unfortunately, conventional composite materials have never satisfied those requirements.
For example, sliding bearing is used with various kinds of machine tools, or a relative slide face of an actuation mechanism. In view of usage, each of the lubricants is selected, however, depending upon using objects or incorporating positions, the lubricant oil could not always be supplied. As a countermeasure thereto, a bearing having self-lubrication has been developed, and especially bearings have been proposed which are scattered with a solid lubricant such as carbon or molybdenum disulfide in the matrix when dispersion of oil should be avoided, and endurance is required against high compression load.
As a method of scattering solid lubricant into the matrix material, the solid lubricant of bush type is incorporated under pressure into a mother material. In this method the mother material composed of a molten-solidified material is processed with borings, into which solid lubricant independently made is buried, a limitation is inherently provided to increasing the friction coefficient due to restraint of spaces between borings, and a close lubricant face could not formed overall. In addition, it takes a great deal of manufacturing, and requires troublesome machining processes at high cost.
Further, another method is a powder metallurgical manner which scatters solid lubricants into the matrix. Conventionally, if a large quantity of the solid lubricant were contained, formability, sintering property and strength would be exceedingly lowered, and the containing maximum was 15 wt% and practically it was about 10 wt%. Therefore, the introduction system under pressure of said solid lubricant of the bush type was generally employed.
On the other hand, the grinding materials (grinders) are much used for a lapping, super finishing process or super precision finishing by grinding fine notches or slits, which heighten flattening degree of pre-processed works of hard brittle materials such as ceramics or ultra hard alloy, and in general the the ground powders such as diamond, CBN, alumina or others are binded by the binder. In the binders, there are metallic and non-metallic binders, and the former is better in the binding force than the latter and is used for binding of the ground powders of high property such as diamond or CBN.
As manufacturing processes of the grinding materials where the binder is metal as said, there are an electrodeposit process and a sintering process. However, they have problems as follows.
One of the problems is that an amount of grinding powders contained is low. The amount grinding powders contained should be as large as possible for increasing the property of the grinding material. But since the electrodeposit process firmly adheres the grinding powders to the matrix composed of the molten-solidified material by means of nickel plating, the deposited layer is the only one formed, and therefore the amount of the grinding powders contained is limited in itself. With respect to the sintering process, if a large quantity of grinding powders were contained, it would remarkably decrease uniformity of mixture (non-separation), formability and sintering property, and practically the contained amount is around 10 wt% at most.
The other problem is the dispersing property and the holding strength of the grinding powders. Those two elements are important to the grinding materials, but the foregoing processes have not satisfied them. Especially, in the sintering process, the grinding powders are not easily dispersed due to the difference in specific gravity or in grain size between the grinding powders and the ground grains. Further, since the grinding powders gather in spaces between the grains, the holding force thereof is decreased and the grinding powders easily drop out from the matrix during use. Such phenomena often happen, if the grain size of the grinding powders is small, and decrease the mechanical strength of the grinding material in addition to said unsatisfaction of the sintering property.